How displacement analysis may aid fault risking strategies for CO₂ storage

Abstract

Developing an accurate understanding of the ways in which faults have grown within a particular region and stratigraphy can aid risk management for CO2 storage sites. Areas of fault interaction lead to differences in the stress field, resulting in an increased strain, which is often accommodated by a high intensity of deformation bands and/or fracturing, dependent on host rock properties. These structures alter the permeability surrounding faults. Hence, detecting areas of interaction of structures throughout the fault growth history allows the identification of locations where high risk may occur in terms of the hydraulic properties of a fault zone. The Vette Fault Zone (VFZ), bounding the Alpha prospect within the potential CO2 Smeaheia storage site, Northern Horda Platform, is shown to have grown from a minimum of seven fault segments. By utilising a comparison with the adjacent Tusse Fault Zone (TFZ), we can identify potential areas of high risk, where fluids may have the ability to flow across or along the VFZ. The high seal strength of the TFZ holding back a large gas column is likely to be created by shale juxtaposition and smearing with cataclastic processes. The same could be assumed for the VFZ, associated with similar tectonics and displaced stratigraphy. However, rather than membrane breaching causing fluids to flow across the fault, potential areas of high risk have been identified at locations of relict breached relay zones, where the initial displacement of the intersecting faults and area of overlap was high. These areas appear to correspond with the location of hydrocarbon contact depth (spill point) along the TFZ. Using the same assumptions for the VFZ, we can observe one potential area of high risk, which lies within the area of suggested CO2 accumulation.

The Role of Normal Fault Growth History in Influencing Fault Seal Potential, Samson Dome, Offshore Norway

“…The value of considering the fault growth history in assessing the potential of faults to seal or leak fluids has recently received increased interest (e.g., Reilly et al, 2017;Song et al, 2020;Michie & Braathen, 2023). While assessing present-day juxtaposition relationships and fault sealing potential is a valuable approach when considering reservoir behaviour over relatively short (i.e., a few tens of years) production timescales, it does not capture the changes that may occur to fault hydraulic properties over longer, geological timescales (e.g., Manzocchi et al, 2010;Reilly et al, 2017).…”